| Type: | Domain | Name: | Transketolase, N-terminal |
| Description: | Transketolase (TK) catalyzes the reversible transfer of a two-carbon ketol unit from xylulose 5-phosphate to an aldose receptor, such asribose 5-phosphate, to form sedoheptulose 7-phosphate and glyceraldehyde 3- phosphate. This enzyme, together with transaldolase, provides a link betweenthe glycolytic and pentose-phosphate pathways. TK requires thiamine pyrophosphate as a cofactor. In most sources where TK hasbeen purified, it is a homodimer of approximately 70 Kd subunits. TK sequences from a variety of eukaryotic and prokaryotic sources [, ] show that theenzyme has been evolutionarily conserved. In the peroxisomes of methylotrophic yeast Pichia angusta(Yeast) (Hansenula polymorpha), there is a highly related enzyme, dihydroxy-acetone synthase (DHAS) (also known as formaldehyde transketolase), which exhibits a very unusualspecificity by including formaldehyde amongst its substrates.1-deoxyxylulose-5-phosphate synthase (DXP synthase) [] is an enzyme so farfound in bacteria (gene dxs) and plants (gene CLA1) which catalyzes the thiamine pyrophosphoate-dependent acyloin condensation reaction between carbonatoms 2 and 3 of pyruvate and glyceraldehyde 3-phosphate to yield 1-deoxy-D- xylulose-5-phosphate (dxp), a precursor in the biosynthetic pathway toisoprenoids, thiamine (vitamin B1), and pyridoxol (vitamin B6). DXP synthase is evolutionary related to TK. The N-terminal section, contains a histidine residue which appears to function inproton transfer during catalysis []. In the centralsection there are conserved acidic residues that are part of the active cleft and may participate in substrate-binding [].This family includes transketolase enzymes and also partially matches to 2-oxoisovalerate dehydrogenase beta subunit . Both these enzymes utilise thiamine pyrophosphate as a cofactor, suggestingthere may be common aspects in their mechanism of catalysis. | Short Name: | Transketolase_N |
